This invention relates to chemical ablation of metal halide salt and includes, in particular etching as well as cutting alkaline earth metal halide as single crystal barium fluoride.
Metal halides especially single crystal alkaline earth metal halides, have application as insulators, windows and substrates in devices such as photovoltaic diodes, lasers, transistors and charge coupled devices. For example, single crystal barium fluoride is used as a substrate with Group Iv-VI semiconductor diodes to provide detectors of infrared radiation in thermal imaging systems (see, for example, U.S. patent application Ser. No. 781,377, filed Mar. 25, 1977, now U.S. Pat. No. 4,080,723 which is herein hereby incorporated by reference).
When employing metal halide salt such as single crystal barium fluoride as a substrate for such diode devices or in other applications, it becomes necessary at times to etch, cut or otherwise ablate a portion of the salt. In the past, this has been accomplished mechanically as by cleaving along certain crystal planes or sawing with diamond impregnated blades (see U.S. Pat. No. 3,935,302, column 4, lines 52-55). In making thermal imaging systems, as above noted, one current concern is removal of the unworked periphery of single crystal substrates having a center section of diode elements so as to maximize effective operating area. Use of diamond impregnated blades to mechanically saw the substrate perifery, however, can cause undesired chipping, cracking, etc. that result in loss of the usefulness of the device after it has had substantial processing.